1. Field of Invention
The present invention relates to spectrometer for analyzing radiation. More particularly, the present invention relates to a spectrometer that utilizes a capillary array and a dispersive element to generate two-dimensional spectral images of radiation sources.
2. Description of Related Art
In the fields of fusion research, pulsed power physics, and hot, dense plasma physics, it is important to observe and measure emitted radiation. Observations of emitted radiation are a highly useful means by which data may be obtained in these fields. For example, in hot, current carrying plasma devices, such as Z-pinch devices, measurements of emitted radiation can help determine which plasma configurations result in optimum plasma and energy confinement and which configurations will result in the greatest intensity, hardness, stability, and reproducibility of x-ray emissions.
Measurement of short wavelength radiation, such as extreme ultraviolet (EUV), soft x-rays (SXR), and x-rays, is the dominant means for investigating hot, dense plasmas because this is the most feasible way of observing the plasma and because x-ray emissions are closely correlated with plasma dynamics. Short wavelength spectroscopy can be used to accurately measure plasma density, temperature, flow, charge states, atomic processes, and magnetic fields.
There is a strong need for improved spectroscopic measurements to further the understanding of hot, dense plasmas. The prior art has failed to provide a suitable means for generating two-dimensional images of emitted radiation. Two-dimensional images aid the understanding of the spatial distribution of energy in a plasma and help determine consistency between pulses. The prior art has failed to provide a means for simultaneously observing a broad spectrum of short wavelength radiation. Measurements of a broad range can be used to accurately determine electron energy distribution and to simultaneously observe a variety of atomic processes. The prior art has also failed to provide a means for observing emitted radiation at specific times or intervals during an event. Observations taken at specific times are useful in determining the stability of a plasma and understanding the changes of a plasma over a period of time.
The most widely used prior art spectroscopic method utilizes polychromatic and monochromatic imaging. Monochromatic images taken on one or several spectral lines are used to compile two-dimensional maps of relevant plasma parameters (electron density and electron temperature). A spatial resolution of better than 10 .mu.m can be achieved. This resolution, however, is restricted to object fields of limited size. For extended sources, such as a z-pinch apparatus, the average distortion of an image generally increases up to 100 .mu.m or more for plasma columns between 20 and 50 mm in length.
To understand a plasma configuration so that it may be controlled efficiently, it is important to obtain a high-resolution x-ray and EUV imaging. The present invention, described here as a multi-band two-dimensional imaging spectrometer with time framing for rapidly evolving, spatially distributed EUV and x-ray sources, particularly z-pinch type, must meet several constraints.
An essential requirement is a spatial resolution .DELTA.r.ltoreq.50-100 .mu.m in any point of a plasma column and a temporal resolution to at least the time of character scale of compression of a z-pinch, which is as short as several nano second. In order to achieve this, a time-framing technique (e.g., microchannel plates (MCP)) is necessary. In the particular context of goals of investigations of z-p inch or laser plasma sources of radiation, there had to be spectral resolution of .lambda./.DELTA..lambda. more than 500-700 for .lambda..apprxeq.1.0-2.0 nm and more than 800-1500 for .lambda.&lt;0.3-0.6 nm to discriminate between the resonance line and the intercombination and satellite lines of He- like ions in plasma, and there had to be a provision to monitor more than one line to obtain spatially resolved maps of T.sub.e and N.sub.e from line intensity ratios. It is very informative to measure these spectra of the ions of plasma in several spectral bands simultaneously, which correspond to different electron shells of ions (for example, K-shell in x-ray region and L-shell radiation of Ar z-pinch plasma ions).
The described diagnostic apparatus images more than one spatial dimension in more than one spectral band, overcoming two of the main limitations of current state-of-the-art imaging spectroscopy. The multi-band two-dimensional imaging spectrometer, that is described herein, is based on the application of a glass capillary converter (GCC). The GCC consists of a bundle of glass or quartz capillaries. EUV, soft x-ray, and x-ray radiation (spectral range 0.01 nm to 100 nm) are guided along the straight or slightly curved capillaries by multiple grazing-incidence reflections from the inner capillary surface. The GCC can concentrate, guide, and focus short wavelength radiation, and also filter hard x-ray radiation (by at least two orders of magnitude). The transmission of radiation along the quartz capillary has smooth spectral dependence upon wavelength, excluding the two downfalls at K-edges of Si (.lambda.=0.67 nm) and of O (.lambda.=2.3 nm). Previously, GCCs have been used in plasma diagnostics as hard x-ray filters in pinhole chambers, as a device to enhance the flux density of x-ray and EUV radiation on the entrance slit of a monochromator (by two orders of magnitude), and proposed as an x-ray streak camera element. Also GCC has been used in new types of polarimeters/spectrometers for EUV, SXR and x-ray radiation.
Table 1 presents the characteristics of existing x-ray and EUV imaging spectrometers together with the characteristics of the present invention.
TABLE 1 __________________________________________________________________________ Characteristics of Short Wavelength Spectrometers Type 1 2 3 4 5 6 7 __________________________________________________________________________ 1. flat crystal 1-25 0.1-0.2 100-1000 100 20* - + or MLM (25-200) .apprxeq.100** 2. convex crystal 1-25 1 100-1000 100 20* + + or MLM (25-200) .apprxeq.100** 3. Johann scheme 1-25 0.05-0.2 1000- -- 20* - + with crystal 1000 .apprxeq.100** or MLM (25-200) 4. 2D spect-ph 1-25 0.05-0.2 1000 100 10-15* - + with crystal .apprxeq.100** or MLM (25-200) 5. microscope 1-25 0.01 - 1-10 1-10 - + with crystal or MLM (50-200) 6. New system 1-200 several 500-1500 50-100** 50-100** + + with GCC regions __________________________________________________________________________ 1. Spectral range (.ANG.) 2. Relative spectral range (HD max - HD min)/2(HD max + HD min). 3. Spectral resolution .DELTA. 4. Spatial resolution in direction of dispersion (.mu.m). 5. Spatial resolution in transverse to dispersion (.mu.m). 6. Possibility of temporal measurements of lines intensity inside whole spectral region of system during one shot of plasma device. 7. Possibility of temporal measurements of single lines intensity during one shot of plasma device. *for small size source as laser plasma flame **for long plasma column source as zpinch